The present invention relates to a battery system comprising a hybrid battery and an inverter which is connected at the input end to the battery. The invention also relates to a method for operating an inverter which is connected at the input end to a hybrid battery. Furthermore, the invention relates to a vehicle comprising such a battery system and an electric motor which is connected at the output end to the inverter.
The prior art discloses NPC inverters which have at least three voltage levels and are also referred to as neutral point clamped diode multilevel inverters (NPC) having at least three voltage levels. Such an NPC inverter having a number n of voltage levels is supplied with electrical energy via n−1 voltage sources or energy storage sources. The DC voltages generated by the voltage sources or energy storage sources are each made available at the input end to the NPC inverter via a suitable intermediate circuit as a corresponding intermediate circuit voltage. In this case, the intermediate circuit voltages must be tuned since the intermediate circuit voltages must be the same. The intermediate circuit voltages can be tuned either actively or passively by means of hardware or via suitable space vector modulation by means of software. In the case of such NPC inverters, transistors which belong to the same semiconductor technology are used as semiconductor switches.
In a modern hybrid battery system, different energy storage sources of a hybrid battery used can be electrically passively linked to one another, that is to say can be connected in parallel or possibly also in series with one another. Such different energy storage sources can also be electrically actively linked to one another, for example via a DC-DC converter.
With inverters whose semiconductor switches are arranged in a B6 bridge and which are nowadays used when connecting different energy storage sources, different energy storage sources, which occur in hybrid battery systems for example, can be used only to a limited extent. This is the case, on the one hand, the efficiency of a hybrid battery formed from different energy storage sources fluctuates very greatly over an entire operating range of an electric motor operated using such an inverter and is relatively low, on the other hand. It is also disadvantageous that the failure of an individual energy storage cell or of an individual switch results in the failure of an entire electrical drive train of an electric motor supplied with electrical energy by the hybrid battery. All energy storage cells of the energy storage sources are also always used to energize the electric motor even if they are not needed to produce a voltage level required by the electric motor. This has a disadvantageous effect on the service life of the energy storage cells.